1. Field of the Invention
The invention concerns compatible polymer blends of a polymer component which contains cyclohexyl (meth)acrylate as the monomer and a polymer component which contains .alpha.-methyl styrene as the monomer.
2. Discussion of the Background
As a rule, different polymer species are considered to be incompatible with one another, i.e. different polymer species generally do not form a homogeneous phase, which would be characterized by complete miscibility of the components, down to slight proportions of a component. Certain exceptions to this rule have caused increasing interest, particularly among the experts concerned with the theoretical interpretation of the phenomena.
Completely compatible mixtures of polymers demonstrate complete solubility (miscibility) in all mixture ratios. As evidence of the miscibility, the glass temperature Tg or the so-called "optical method" (clarity of a film poured from a homogeneous solution of the polymer mixture) is often used as a reference. (See Brandrup-Immergut, Polymer Handbook, 2nd edition, III, 211-213).
As a further test for the miscibility of polymers which are different from one another, the occurrence of the lower critical solution temperature (LCST) is used. (See DE-A No. 34 36 476.5 and DE-A No. 34 36 477.3). The occurrence of the LCST is based on the process which occurs during warming, where the polymer mixture, which has been clear and homogeneous until then, separates into phases and becomes optically cloudy to opaque. This behavior is a clear indication, according to the literature, that the original polymer mixture had consisted of a single homogeneous phase which was in equilibrium. Examples of existing miscibility are represented, for example, by the systems polyvinyl fluoride with polymethyl methacrylate (PMMA) or with polyethyl methacrylate. (U.S. Pat. Nos. 3,253,060; 3,458,391 and 3,459,843). Recent results concerning "polymer blends" and possible applications for them were reported by L. M. Robeson in Polym. Engineering & Science, 24 (8), 587-597 (1984).
Copolymers of .alpha.-methyl styrene, maleic acid anhydride, as well as of .alpha.-methyl styrene and acrylonitrile are compatible with polymethyl methacrylate under certain conditions. Compatibility is also found in certain binary and ternary systems of copolymers of acrylonitrile with vinyl acetate and .alpha.-methyl styrene (C. Vasile et al., Chem. Abstr. 90: 39511a). Compatibility of copolymers of .alpha.-methyl styrene and acrylonitrile also exists with polymethyl methacrylate. In contrast, poly-n-propyl methacrylate, poly-isopropyl methacrylate and polycyclohexyl methacrylate are not compatible even with copolymers of .alpha.-methyl styrene and acrylonitrile (See S. H. Goh et al., Polymer Engineering and Science, 22, 34 (1982)).
This means that copolymers of .alpha.-methyl styrene and maleic acid anhydride and copolymers of .alpha.-methyl styrene and acrylonitrile demonstrate behavior similar to copolymers of styrene and maleic acid anhydride and copolymers of styrene and acrylonitrile. While copolymers of styrene and a highly polar monomer (e.g. acrylonitrile, maleic acid anhydride) are compatible with PMMA under certain conditions (e.g. copolymer composition), this is not the case for polystyrene itself.
For example, M. T. Shaw and R. H. Somani indicate the miscibility of PMMA with polystyrene as being only 3.4 ppm (PMMA with a molecular weight of 160,000) or 7.5 ppm (PMMA with a molecular weight of 75,000). See Adv. Chem. Ser. 1984, 206; Polymer Blends Compos. Multiphase Syst., 33-42, Chem. Abstr. 101:73 417e. Other polymethacrylates and polyacrylates similarly do not form transparent polymer blends with polystyrene. This is true, e.g., for polyethyl acrylate, polybutyl acrylate, polyisobutyl methacrylate, polyhexyl methacrylate See R. H. Somani and M. T. Shaw, Macromolecules, 14, 1549-1554 (1981).
Mixtures of poly -.alpha.-methyl styrene and poly(meth)acrylates behave in a similar manner. For example, according to W. A. Kruse et al, Makromol. Chem. 177, 1149-1160 (1976), polymethyl methacrylate cannot be mixed with poly -.alpha.-methyl styrene with molecular dispersion.
Our own experiments show that poly -.alpha.-methyl styrene demonstrates compatibility with polymethyl acrylate and polymethyl methacrylate at room temperature. When heated to approximately 130.degree. C., however, de-mixing occurs. In other words, these polymer mixtures demonstrate LCST behavior (LCST=lower critical solution temperature). A certain, slight compatibility is also found with polybutyl methacrylate. Here, the LCST is approximately 80.degree. C. in the mixture example studied. This therefore indicates that the compatibility decreases with an increasing chain length of the ester groups, as was also described for the polymer mixtures: copolymers of .alpha.-methyl styrene and acrylonitrile/polymethyl acrylates. See S. H. Goh et al., Polymer Engineering and Science, 22, 34 (1982).
Mechanical mixtures of polymers (polyblends) have resulted in plastic products with improved properties in certain cases and in certain areas of the plastics industry (See Kirk-Othmer 3rd edition, Vol. 18, pp. 443-478, J. Wily, 1982). The physical properties of such "polyblends" generally represent a compromise, which can mean an overall improvement as compared with the properties of the individual polymers. In these situations, multi-phase polymer mixtures have achieved much greater commercial significance than compatible mixtures (See Kirk-Othmer, loc. cit., p. 449). Multi-phase and compatible mixtures must therefore be kept strictly separate with regard to both their physical properties and their properties which are relevant for application technology, especially their optical properties (transparency, clarity, etc.). As already explained, a lack of compatibility often sets narrow limits for the goal of thereby achieving an improved overall spectrum of properties. This also appeared to apply to the two polymer classes of polystyrenes and polyalkyl (meth)acrylates. See W. A. Kruse et al., Makromol. Chem. 177, 1145 (1976) as well as R. H. Somani and M. T. Shaw, Macromolecules 14, 1549-54 (1981).